Apparatus for the continuous dendritic growth of crystalline material



y 1965 R. LONGINI ETAL 3,194,637 APPARATUS FOR THE CONTINUOUS DENDRITIC GROWTH OF CRYSTALLINE MATERIAL Filed June 22, 19 60 3 Sheets-Sheet 1 INVENTORS Richard L. Longini, Allen I. Bennefi, Walter J. Smith, Jacob J.Colemun y 1965 R. L. LONGINI E'l'AL 3,194,637

APPARATUS FOR THE CONTINUOUS DENDRITIC GROWTH OF CRYSTALLINE MATERIAL 3 Sheets-Sheet 2 Filed June 22, 1960 July 13, 1965 R. L. LONGINI ETAL 3,194,637

APPARATUS FOR THE CONTINUOUS DENDRITIC GROWTH OF CRYSTALLINE MATERIAL Filed June 22, 1960 3 Sheets-Sheet 3 ,4 94 93 REEL MOTOR MOTORSPEED CHAMBER DRIVE CONTROLLER :1 ll

FURNACE POWER CHAMBER GENERATOR Flg. 5

TEMPERATURE I HEATING,

SENS'NG CONTROLLER APPARATUS 4 97 4s REEL C VACUUM CHAMBER PUMP r95 2 I00 PROTECTIVE 96 r 99 I ATMOSPHERE FuRNAc VACUUM SUPPLY CHAMBER PUMP United States Patent 3,194,637 APhARATUS FOR THE (JQNTWUOUS DENDRiT- IC GRQWTH 0F CRYSTALLENE MATERIAL Richard L. Longini, Pittsburgh, Allan 1. Bennett, Export, Walter J. Smith, Monroeviile, and Jacob 3. Coleman, Braddock, Pa, assignors to Westinghouse Electric 60rporation, East Pittsburgh, Pa, a corporation of Pennsylvania Filed June 22, 196i), Ser. No. 37,931 9 Claims. (Cl. 23273) The present invention relates generally to apparatus for the continuous dendritic growth of crystalline material and more particularly relates to apparatus for the continuous dendritic growth of a semiconductor crystal of great length.

In practicing the dendritic growth of a semiconductor such as germanium, silicon or gallium arsenide it is frequently desirable to produce very long, dendritic crystal strips, for example 100 or more feet long.

Conventional or Czochralski apparatus for producing a crystal of solid material includes means for contacting the surface of a melt of the solid material with a previously prepared crystal or seed of the material and slowly withdrawing the prepared crystal. The seed pulls after itself a portion of the melt which solidifies on the seed thereby drawing a large ingot crystal of some length, to 6 inches from the melt. Conventional apparatus is limited as to the length of crystal that can be drawn because of the size of the crystal and the limited crucible volume available for containing a melt.

Accordingly, the principal object of the present invention is to provide apparatus for producing dendritic crystal strips of extended lengths.

Another object of the present invention is to provide apparatus for the continuous growth of dendritic crystalline material.

Another object of the present invention is to provide apparatus for readily storing said dendritic crystal strip as it is pulled from the melt.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing in which:

FIGURE 1 is an elevational view, partly in section, of an illustrative embodiment of the present invention;

FIG. 2 is a cross sectional view taken along the line ll-II in FIG. 1;

FIG. 3 is a somewhat enlarged fragmentary cross sectional view taken along the line llllll in FIG. 1;

FIG. 4 is a fragmentary cross sectional view taken along the line lV-IV in FIG. 3',

FIG. 5 is an electrical circuit diagram for the illustrative embodiment shown in FIG. 1; and

P16. 6 is a flow diagram for the illustrative embodiment shown in FIG. 1.

The present invention comprises a lower or furnace chamber 2 and an upper or reel chamber 4 connected by an interconnecting chamber 6, all of which is supported by a frame member 3. Dendritic crystalline strip which is grown in the first chamber 2 is, in turn, drawn through the interconnecting chamber 6 to the second chamber 4 1 where the strip is stored.

ddhdfid? Patented July 13, 1%65 18 which is integral with the chamber 2. Means for viewing the work area of the furnace chamber 2 is provided by a heavy sight glass 22 of suitable material such as Pyrex. The internal surface of the sight glass 22 is gold coated to reflect infrared rays emanating from within the chamber 2. The sight glass 22 is secured to the chamber 2 by suitable clamps 21 to provide a pressure tight vessel. A second sight glass 24 of suitable material but of smaller thickness is supported in the chamber 2 by means of channels 26 and is utilized to protect the gold coating of glass 22 and partially absorb heat from the chamber 2. Heating means for transforming the crystalline material within the crucible 10 to a supercooled melt is provided by a heating coil 30. The input power to the heating coil 39 is controllable to prepare a melt of material within the crucible lit) at a temperature slightly above the melting temperature. Upon contacting the melt with the seed and after a suiiicient period of time to cause wetting of the lower surface of the seed, the heat input to the melt is reduced so that the melt is supercooled. By controlling the degree of supercooling and the rate of withdrawing the seed crystal from the melt, the thickness of the dendritic crystal pulled can be regulated. A sapphire rod light pipe 27 is passed through the trap disc 24 and up into the crucible it to sense the temperature in the crucible l0 and provide a signal to a temperature sensing device 28 such as a radiation pyrometer shown secured to the bottom of the disc 14 by means of a mounting flange 29. The temperature sensing device 28 provides a signal which is used to control input power to coils and thus the temperature of the crucible it).

The upper or reel chamber 4 more particularly comprises a front half-shell t2 and a rear half-shell 44 pivotally secured to join together forming a pressure tight chamber. The front and rear half-shells 42 and 44 include heavy ring members 43 and 45 respectively. An annular ring 46, mounted over the ring member 45 and disposed to extend over the ring member 43 when the front half-shell d2 meets the rear half-shell 44, is adapted to rotate relative to the ring members 43 and 45 and lock the half-shells into place by means of inclined planes machined onto a series of teeth 4'7 on the annular ring 46 and a second series of teeth 48 on the heavy ring member 43 but offset from the first series of teeth. The front and rear half-shells 42 and 44, respectively, are ellipsoidal in shape to withstand high internal pressures and when joined together provide a clam-shell like appearance. An O-ring 49 positioned between the heavy ring members 43 and 44 seals the chamber 4 when the shells are close.

A windup reel 59 and a tape supply roll or reel '70 are mounted on a frame dill within the reel chamber 4. The reels 5i) and 74) are herein shown to be mounted in parallel planes and displaced centers of rotation. However, it is to be understood that any suitable disposition of one reel relative to the other may be used.

The windup reel 50 is rotatably mounted on the frame Stl by means of socket mounted ball bearings 52 peripherally spaced to engage the inner circumference of the windup reel 50. Means for rotating the windup reel 58 is more clearly demonstrated in FIGS. 3 and 4 wherein a drive shaft 53 extends through the frame member 86 and has mounted at one end thereof a disc member 54 having at its outer periphery a resilient ring 55 for engagement with the circumferential edge of the windup reel 5%). A bracket 56 supports the opposite end of the drive shaft 53. A helical gear 57 rotatably mounted on the drive shaft 53 and a helical gear 558 shown disposed at right angles to the helical gear 57 are driven by a drive shaft 59 extending through the rear half-shell 44- for con nection to a suitable driving means such as an electric -by Way of illustration.

'tape supply roll in position. provides a tape 75 made, for example, of plastic or other 3; motor. A gasket 60 maintains the pressure tight seal within the upper chamber 4. It is to be understood, however, that any suitable means for driving the windup reel 5t may be used and the arrangement shown is only An interconnecting chamber 6' connects the lower chamber 2' and upper chamber 4. The windup reel 59 is provided with a leader 62 secured at one end and wound on the windup reel. A prepared crystal or seed of the crystalline material is secured at the opposite end :of the leader 62 by any suitable means such as tape 64-.

If available, a length of dendrite crystal may be used so that no leader 62 is necessary. The leader 62 positions the seed into engagement with the surface of the melt within the crucible 10..

The tape supply reel 70 is adapted to rotate on the frame member 80 by means of peripherally spaced rollers 71, each having an annular flange 72 for holding the The tape supply roll 79 suitable material which is wound as an interlayer between adjacent layers of the wound dendritic strip. To play on the tape '75 from the roll 7t? a drum 76 of selected tapers is secured to the base member 89 by means of a pin 77. The drum 76 changes the direction of the tape being unwound from the tape supply roll 70 and .positions the tape to take its position adjacent the dendendrite crystal being drawn allows the drawn crystal to .be pulled substantially perpendicular to the surface of the melt within the crucible 10. The curved surface and the windup reel gently bends the dendrite crystal to lie' down on the curved surface presented by the windup reel 50. 7

An idler roll 66 pivotally mounted to the frame member 80 by means of a peg 67 urges the dendrite crystal and tape against the curved surface presented by the windup reel 50. The curved surface of the windup reel 50 has such a radius as to provide a surface for laying down the dendrite crystal without causing the crystal to be bent sufliciently to exceed its breaking point.

The reel on which the dendrite is wound, and the reels vand guides used to direct the dendrite, are so arranged thatthe dendrite below the reel and the guide is substantially merely straight and vertiual to avoid breakage of the dendrite or rubbing of the dendrite against the walls of the shell.

Should a protective atmosphere be required within the chambers 2 and 4, a suitable inlet 81 is provided to the lower chamber 2. Preceding .the inlet 81 may be an inlet valve and purifying means such as cold and hot traps, not illustrated. Exit means in the form of a vent 82 leading to an outlet valve and additional purifying means, not illustrated, may provide for circulating a current of such protective atmosphere through the furnace chamber 2, the interconnecting chamber 6 and the reel chamber 4. When desirable, the flow of protective atmosphere may be reversed. The additional advantage in v reversing the flow of protective atmosphere is that gaseous products from the melt will not readily diifuse to the upper chamber where the dendrite crystal is formed when the protective atmosphere current is opposing suchdiffusion. The interconnecting chamber is also selected to prevent diffusion from one chamber to the other by being deliberately formed to have a long passageway of small cross-sectional area to inhibit the interchange of gaseous products between the furnace and reel chambers. In this manner, the interconnecting chamber contains the impurities within the lower chamber.

The apparatus in accordance with the present invention is equally adaptable to drawing a dendritic crystalline strip in a vacuum as Well as under pressure. When the apparatus is being evacuated for purposesof operation in a vacuum or upon purging of the protective atmosphere, care must be taken to insure that the difference between the rate of evacuation of the furnace or lower chamber 2 and that of the reel chamber or upper cham ber 4 shall not cause gas flow through the interconnecting chamber 6 which is sufiiciently rapid and violent to break the dendrite crystal therein.

Referring to the circuit diagram of FIG. 5, it canbe seen that power brought into the lower or furnacechamher 2 to the coil Ed is controlled by the electric heating 'controller and power generator 91 which. provides power to the heating coil 30 within the furnace chamber 2. One such controlleris as described'and claimed in a copending application Serial No. 22,076, filed April 7, 1960, by A. 1. Bennett and R. L. Longini. Temperature sensing apparatus 92 determines the variation of temperature within the furnace chamber from a desired level and feeds back a signal to the electric heating controller 90 to regulate power from the generator 91 and thus in turn power to the coil in the furnace chamber.

To control the speed with'which the windup reel 5ft draws the dendrite crystal from the supercooled melt, a motor speed controller 93 varies the speed of a motor drive 94 which is, in turn, connected to the drive shaft 59 entering the upper chamber 4 and hence to the driving reel 50 by means of the gearing arrangement previously described and discussed.

If a protective atmosphere is to be supplied within the furnace chamberand reel chamber, then a protective atmosphere supply source 95 is required with sufficient source pressure for forcing such protective atmosphere temperature of the melt such as arsenic when crystals of gallium arsenide are being pulled, a separate heating means, not illustrated, maybe disposed around the lower chamber 2 so that the chamber 2 may be suitably heated. For example an electrically heated cover or jacket may be disposed to maintain'the walls of the furnace chamber 2 at a temperature sufficient to prevent condensation of arsenic thereon.

The apparatus is heavily constructed to withstand any desired type of operationchosen from'a variety of dendritic crystal materials which may be pulled by the apparatus. For example, when pulling crystals of gallium phosphide having a partial pressure of phosphorus of about 10 atmospheres at the compound melting point, the chambers must be pressurized to that extent for successful operation.

Thus, it is readily apparent that the present invention provides apparatus for the growth of very long dendritic crystal strips. By selecting the curved surface of the windup reel 50, and disposing the first and second chambers and the windup reel 50 that the crystalline strip being drawn may have a straight and vertical path from the furnacechamber 2, breakagev of the dendrite is avoided.

Should the power generator 91 be of the RF or electron bombardment type, it is advantageous to line the interconnecting chamber 6 with an electrical insulating material such as glass to prevent the dendritic strip from accidentally making electrical contact with the conducting metal wall of the interconnecting chamber 6.

The present apparatus has been successfully operated and has provided dendritic crystal strips of exceptionally long lengths, for example, 300 feet. The thickness of the dendritic crystal being drawn can be readily controlled by the speed at which the windup reel 50 is rotated Within the reel chamber 4 and the temperature of the crucible 10.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications, alterations and substitutions within the spirit and scope of the present invention are herein meant to be included.

We claim as our invention:

1. Apparatus for the continuous growth of dendritic crystalline material comprising a first air tight chamber, a crucible mounted within said first chamber for containing a melt of said material; heating means for con trolling the temperature of the melt disposed about the crucible; a second air tightchamber disposed above said first chamber; a third chamber interconnecting said first and second chamber; windup means rotatably mounted within said second chamber and presenting a curved surface; said windup means disposed within said second cham her to align the dendrite crystal issuing from said first chamber with a portion of said curved surface; said windup means including means for seating and drawing said crystal onto said curved surface.

2. Apparatus for the continuous dendritic growth of crystalline material comprising a first air tight chamber; a crucible mounted within said first chamber for containing a melt of said material; heating means for controlling the temperature of the melt disposed about the crucible; a sec ond air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of the crystal from said first chamber to said second chamber; a windup reel rotatably mounted within said second chamber; a tape supply reel adapted to rotate within said second chamber for supplying a buffer tape; means attached to said windup reel for seating and drawing said dendrite crystal onto said windup reel; means for securing the tape from said tape supply reel and playing it off said supply reel to said windup reel whereby the tape is wound on the windup reel as an interlayer between adjacent layers of the wound dendritic crystal.

3. Apparatus for the continuous dendritic growth of crystalline material comprising a first air tight chamber; a crucible mounted within said first chamber for containing a melt of said material; heating means for controlling the temperature of the melt disposed about the crucible; a second air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of the crystal from said first chamber to said second chamber; conduit means for providing a suitable protective atmosphere within said chambers; a windup reel rotatably mounted within said second chamber; a tape supply reel adapted to rotate within said second chamber for supplying a buffer tape; means attached to said windup reel for seating and drawing said dendrite crystal onto said windup reel; means for securing the tape from said tape supply reel and playing it oif said supply reel to said windup reel whereby the tape is Wound on the windup reel as an interlayer between adjacent layers of the wound dendritic crystal.

4. Apparatus for the continuous dendritic growth of crystalline material comprising a first air tight chamber; a crucible mounted within said first chamber for containing a melt of said material; heating means for controlling the temperature of the melt disposed about the crucible; a second air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of the crystal from said first chamber to said second chamber; said interconmeeting third chamber being insulated from making electrical contact with said crystal; a windup reel rotatably mounted within said second chamber; a tapesupply reel adapted to rotate within said second chamber for supplying a buffer tape; means attached to said windup reel for seating and drawing said dendrite crystal onto said windup reel; means for securing the tape from said tape supply reel and playing it off said supply reel to said windup reel whereby the tape is wound on the windup reel as an interlayer between adjacent layers of the wound dendritic crystal.

5. Apparatus for the continuous dendritic growth of crystalline material comprising a first air tight chamber; a crucible mounted within said first chamber for containing a melt of said material; heating means for controlling the temperature of the melt disposed about the crucible; a second air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of the crystal from said first chamber to said second chamber; conduit means for providing a suitable protective atmosphere within said chambers; said interconnecting third chamber being relatively long and narrow so that gaseous products shall not readily diffuse from the first chamber to the second chamber; a windup reel rotatably mounted within said second chamber; a tape supply reel adapted to rotate within said second chamber for supplying a buffer tape; means attached tosaid windup reel for seating and drawing said dendrite crystal onto said windup reel; means for securing the tape from said tape supply reel and playing it off said supply reel to said windup reel whereby the tape is wound on the windupreel as an interlayer between adjacent layers of the wound dendritic crystal.

6. Apparatus for the continuous dendritic growth of crystalline material comprising a crucible for containing said material; heating means for transforming said material to a supercooled rnelt disposed about said crucible; a first air tight chamber for containing said crucible and heating means; a second air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of said dendrite crystal from said first chamber to said second chamber; a tape supply reel adapted to rotate within said second chamber; a driven reel rotatably mounted within said second chamber and presenting a curved surface in the path of the dendrite crystal issuing from said first chamber; means attached to said driven reel for drawing and winding said crystal onto said driven reel; a drum interposed between said tape supply reel and said driven reel for aligning said tape for wrapping around said curved surface; and an idler adapted to rotate within said second chamber to Wrap said dendrite crystal and interlayer tape on said curved surface.

'7. Apparatus for the continuous dendritic growth of crystalline material comprising a crucible for containing said material; heating means for transforming said material to a supercooled melt disposed about said crucible; a first air tight chamber for containing said crucible and heating means; a second air tight chamber disposed above said first chamber; a third chamber interconnecting said first and second chamber and allowing for the passage of said dendrite crystal from said first chamber tosaid second chamber; a tape supply reel adapted to rotate within said second chamber; a driven reel rotatably mounted within said second chamber and presenting a curved surface in the path of the dendrite crystal issuing from said first chamber; means attached to said driven reel for drawing and Winding said crystal onto said driven reel; means for driving said driven reel; said means including a drive shaft extending through said second chamber; a disc member having at its outer periphery a resilient ring for engagement with the circumferential edge of said driven reel and disposed to be driven by said drive shaft; and means at the opposite end of said drive shaft for rotating said drive shaft at a predetermined speed; a drum connecting said first and second chamber and allowing for the passage. of said dendrite crystal from said'first chamber 'to said second chamber; a tape supply reel adapted to rotate within said second chamber; a driven reel rotatably mounted Within said second chamber and presenting a curved surface in the pathof the dendrite crystal issuing from said first chamber; means attached to said driven reel for drawing and winding said crystal onto said driven reel; said driven reel and said tape supply reel are disposed in parallel planes; a drum interposed between said tape supply, reel and said driven reel for aligning said tape for wrapping around said curved surface; and an idler adapted to rotate within said second chamber to wrap said dendrite crystal and interlayer tape on said curved surface.

9. Apparatus for the continuous dendritic growth of crystalline material comprising a crucible for containing said material; heating means for transforming said material to a supercooled melt disposed about said crucible; a first air tight chamber for containing'said crucible and heating means; a second air tight chamber disposed above said first chamber; said second chamber comprising two walls ellipsoidal in shape and butted together in pressure tight relationship; a third chamber interconnecting said first and second chamberand allowing for the passage of said dendrite crystal from said'first chamber to; said second chamber; a tape supply reel adapted to rotatewithin said second chamber; a driven reel rotatably mounted within said second chamber and presentingra curved'surface in the path of the dendrite crystal issuing from said first chamber; means attached to said driven ,reel for drawing and winding said crystal onto said driven reel; a drum interposed between said tape supply reel and said driven reel for aligning said tape for wrapping around said curved surface; andan idler adapted to rotate within said second chamber to wrap said dendrite, crystal and interlayer tape on said curved surface,

References (Iitedby the Examiner UNITED STATES PATENTS Y OTHER REFERENCES LeHovcc et al.: Review of Scientificlnstruments, vol. 24, #8, 8/53, pages 652 to655, Q184.R5.

NORMAN YUDKOFF, Primary Examiner.

I GEORGE D; MITCHELL, MAURICE A. BRINDISI,

' p Examiners. 

1. APPARATUS FOR THE CONTINUOUS GROWTH OF DENDRITIC CRYSTALLINE MATERIAL COMPRISING A FIRST AIR TIGHT CHAMBER, A CRUCIBLE MOUNTED WITHIN SAID FIRST CHAMBER FOR CONTAINING A MELT OF SAID MATERIAL; HEATING MEANS FOR CONTROLLING THE TEMPERATURE OF THE MELT DISPOSED ABOUT THE CRUCIBLE; A SECOND AIR TIGHT CHAMBER DISPOSED ABOVE SAID FIRST CHAMBER; A THIRD CHAMBER INTERCONNECTING SAID FIRST AND SECOND CHAMBER; WINDUP MEANS ROTATABLY MOUNTED WITHIN SAID SECOND CHAMBER AND PRESENTING A CURVED SURFACE; SAID WINDUP MEANS DISPOSED WITHIN SAID SECOND CHAMBER TO ALIGN THE DENDDRITE CRYSTAL ISSUING FROM SAID FRIST CHAMBER WITH A PORTION OF SAID CURVED SURFACES; SAID WINDUP MEANS INCLUDING MEANS FOR SEATING AND DRAWING SAID CRYSTAL ONTO SAID CURVED SURFACE. 